STAT1 and Down syndrome: STAT1 is downstream of type I and II interferon signaling, and STAT1 GOF syndrome was initially discovered as associated with Mendelian susceptibility to mycobacterial disease; however, a large cohort of 274 patients demonstrated a high rate of autoimmunity in ∼37% of patients, including T1D, hypothyroidism, cytopenias, and SLE (90).